This invention relates to systems and methods for removing heat from a system, and in particular, removing heat from bearings or other objects.
Bearings, bushings, and other points of support are used for many different applications requiring support for a rotating body. An example of one such application is an electrical machine such as a generator and/or motor. The rotor of such machines are typically mounted between two bearings, which bear the load of the rotor. During operation of the electric machine, heat may be generated by the stator core, stator windings, bearings, rotor, rotor windings and other sources. Heat may be detrimental to machine performance and operational life. For example, excess heat can decrease the flux capacity of permanent magnets in the machine and damage machine components such as bearings and windings (e.g., stator and rotor windings). In additional respect to bearings, lubricants contained therein may be subject to degradation, burning, or other detrimental effects which may reduce the performance or operational life of the bearing, or destroy it altogether.
Conventional methods for cooling electric machines include auxiliary cooling fans, circulating water systems, and/or circulating oil systems. Other systems may use compressors to route high velocity air as may be needed to achieve desired cooling. Though such cooling systems are able to cool electric machines and components thereof (e.g., bearings), they require substantial maintenance, a supply of power to operate, and can be costly. Moreover, such cooling systems may be limited in their capacity to remove heat from the machine and thus may be unable to maintain an appropriate operating temperature, especially in high speed applications.
One such example of a high speed application in which bearings or other points of support may be used include turbine-generators. A turbine-generator is an electrical machine (e.g., a generator) integrated with a turbine. The turbine may be directly coupled to the rotor shaft of the electrical machine and cause the rotor to rotate when driven by a working fluid (e.g., gas). The rotor shaft may be supported by two or more bearings, such as Model Number SER-201, 13 mm bore by NHBB Corporation of Peterborough, N.H. When grease lubrication is used, this bearing can produce approximately 600 Watts of heat when operating at 70,000 rpm.
Turbine-generators are highly customizable, and may be used in various applications or systems such as, for example, thermal and compressed air storage (TACAS) or compressed air storage (CAS) energy systems. In some TACAS and CAS systems, a micro-turbine-generator, such as a micro-turbine system available from Capstone Turbine Corporation of Chatsworth, Calif. may be used to generate power for a load. A micro-turbine operating in a TACAS or CAS system may operate at high shaft speeds, which is necessary for generating a requisite quantity of power in as small a package as possible, and therefore may require cooling to remove heat from the bearings and other parts of the turbine-generator during operation.
Turbine-generators and other devices requiring bearings may use many different types of bearings, depending on factors such as size, speed, loading requirements, and other suitable factors. Different types of bearings provide different advantages but may have various drawbacks. For example, grease lubricated anti-friction type bearings are highly economical and handle high rotational speeds. This type of bearing may be suitable for use in high-speed turbine-generator applications. However, lubricants contained in anti-friction bearing types may heat up at high speeds and erode, thereby reducing the performance of the bearings. Sleeve type bearings can be economical but may not operate at high speeds. Alternatively, gas lubricated sleeve type bearings are capable of operating at high speeds but are generally not economical.
Accordingly, it would be desirable to provide systems and methods to improve cooling of bearings or other objects.